Norovirus Vax Cuts Severity of GI Symptoms

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Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

SAN FRANCISCO -- A bivalent norovirus vaccine protected patients against severe vomiting and diarrhea symptoms, as well as viral shedding, researchers reported here.

Compared with patients treated with placebo in a phase I/II trial of the vaccine, no patients who received the norovirus vaccine reported severe vomiting and/or diarrhea (0% versus 8.3%), and norovirus symptom severity was significantly reduced among those in the treatment group (20% versus 41.7%, P=0.028), according to David Bernstein, MD, of Cincinnati Children's Hospital Medical Center in Ohio, and colleagues.

At 10 days after receiving the vaccine, fewer patients shed the virus (22.4% versus 36.2%), though this difference was not significant, Bernstein said at a press conference during the IDWeek meeting.

Bernstein and colleagues tested a bivalent norovirus vaccine in a population of 98 adults who were otherwise healthy and intentionally infected with norovirus as part of the randomized, double blind, multicenter, placebo-controlled human challenge trial.

The vaccine was formulated against the GI.1 and GII.4 virus strains, which respectively represent roughly 10% and 64% of strains seen, Bernstein said, adding that "one of the challenges with norovirus and the norovirus vaccine is the diversity of viral strains."

Participants received either two inoculations with vaccine at 28 days apart or placebo, and then received 4,400 RT-PCR units of the GII.4 challenge virus at 56 days from baseline. They were monitored in an inpatient ward for 4 days with no outside contact.

Study endpoints included safety, immunogenicity, and efficacy, which included measures of viral shedding in stool and after 30 days from receiving the virus.

Symptoms were recorded for 4 days after the virus was introduced. Patients self-reported symptom severity.

Moderate to severe symptoms occurred in 6% of patients who were vaccinated versus 18.8% of those who received placebo, though this difference was not significant. Mild, moderate, or severe symptoms occurred in 18% of patients who were vaccinated versus 37.5% of those who receive placebo, which was significant (P=0.042).

Bernstein cautioned that these results were preliminary and that real-world settings would be the next place to test the vaccine. He also said that his team didn't know the length of time the vaccine produced immunity for, adding that "norovirus doesn't change as frequently as the flu, so we hopefully won't need to revaccinate patients every year."

"If we achieve herd immunity and we're exposed to fewer norovirus over our lifetime, we may not need to be boosted as frequently so time will tell," pointed out Andrew Pavia, MD, of the University of Utah Health Care in Salt Lake City.

"The short-term benefits [of the vaccine] are very attractive, even if it doesn't alter long-term susceptibility or lead to the extinction of some of these viruses," added Pavia, who served as session moderator.

Bernstein noted that the four-fold rise in serum antibodies from pre-to-post virus introduction "was an inadequate test for infection" and that it was not achieved in 11 subjects who experienced gastroenteritis. Additionally, viral shedding did not predict symptomatic disease. Finally, the definition of illness that included quality and quantity of vomiting or diarrhea did not align with clinical evaluations of disease.

The study was supported by Takeda Pharmaceufical Company.

The authors received support from LigoCyte, Takeda Vaccines, and the University of Rochester in Rochester, N.Y. Some co-authors are employees of Takeda.

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